Push button switches which emit light to indicate the switching state, e.g., the ON-state, are well known in the art. FIG. 1 is a cross-sectional view of a light emitting push button switch of the type conventionally known and FIG. 2 is a cross-sectional view of the switch taken along line A--A of FIG. 1.
As shown in the figures, an electronic apparatus comprises a casing 1, a printed circuit board 2 fixedly coupled to casing 1 at side portions thereof (not shown) and an operation panel 5. Operation panel 5 is detachably mounted in casing 1 and an information plate (not shown), such as a paper plate carrying written operational instructions, is positioned between operation panel 5 and casing 1. A push button switch is mounted on the electronic apparatus and comprises a button block 6 positioned in through holes formed in casing 1 and operation panel 5, a switching detector 3 mounted on printed circuit board 2 and supporting button block 6 and a light emitting diode (LED) 4 mounted on printed circuit board 2 adjacent switching detector 3. Button block 6 is movable in an upward and downward direction and includes a flange 9 which contacts the surface of casing 1 to limit the upward movement of the button block.
Switching detector 3 comprises an electrode package 3a, including two electrodes, which is disposed on the surface of printed circuit board 2, and a conical elastic body 3b mounted on electrode package 3a and contacting the bottom surface of button block 6. Conical elastic body 3b is formed of rubber and includes a conductive rubber element (not shown) fixedly disposed at the top interior portion of body 3b. Button block 6 is movable and travels upwardly and downwardly responsive to a downward pushing force applied by an operator and an upward return force of body 3b. In operation, when button block 6 is depressed to turn the switch "on", conical elastic body 3b is defected downwardly so that the two electrodes of package 3a are connected through the conductive rubber element of body 3b and LED 4 is activated to indicate the ON-state.
Button block 6 comprises a non-transparency block 7 and a transparency block 8 adhered to block 7 and formed of a rectangular prism. Non-transparency block 7 is disposed on conical elastic body 3b and transparency block 8 is positioned directly above LED 4.
In a conventional switch such as shown in FIGS. 1 and 2, the ON-state is initiated by pushing down once on button block 6 and the OFF-state is entered by pushing down on the button block a second time. In the ON-state, LED 4 emits light which illuminates the bottom surface of transparency block 8. The emitted light then passes through transparency block 8 and is radiated from the top surface 8c (FIG. 2) of the transparency block 8, as explained hereinafter in greater detail. If the switch is used on a desk apparatus, such as a desk telephone, the operator observes top surface 8c from an oblique angle, which is typically about 45.degree. with respect to the surface of operation panel 5, as shown in FIG. 2.
With continued reference to FIG. 2, light is emitted from LED 4 along light paths K--K' and is refracted on the bottom surface of transparency block 8. The refracted light then enters transparency block 8 along light paths L--L' and is reflected by the inside surfaces of transparency block 8. The reflected light is refracted on top surface 8c and is then emitted from top surface 8c along light paths M--M'. K-L-M and K'-L'-M' thus define the respective paths of light that are visible to the operator. Because the width "O" between light paths M and M' emitted from top surface 8c is narrower than the width "P" corresponding to the width of top surface 8c, it is often difficult for an operator to observe light emitted from top surface 8c if the operator views the switch from a 45.degree. angle. This is particularly true if the surrounding area is brightly lighted. In such circumstances, where the light emitted from top surface 8c is not clearly visible, the operator may incorrectly identify the state of the switch.